Cooperative trials in pediatric cancer patients have played a major role in the remarkable improvement in cure of childhood cancers. Because most childhood cancers are rare, it is only through this mechanism that adequate numbers of patients can be accrued in reasonable lengths of time for randomized controlled studies. The Department of Pediatrics at Roswell Park Cancer Institute (RPCI) has actively participated in cooperative group trials via the Pediatric Oncology Group (POG) to answer treatment questions which would be impossible to answer were we to conduct only single institution studies. Some pediatric solid tumors are so rare that national intergroup studies are required. We also participate in these intergroup studies. RPCI investigators are coordinators for a number of POG protocols including front-line studies for the treatment of advanced Hodgkin's disease, advanced small non- cleaved cell lymphoma, non-rhabdomyosarcoma soft tissue sarcomas, acute lymphoblastic leukemia in relapse, the National Wilms Tumor Study, brain tumors in infants, and the Intergroup Ewing's Sarcoma Study. Roswell Park investigators have also developed POG phase II studies of continuous infusion 5-fluouracil and the combination of cisplatin, ifosfamide and etoposide. Roswell Park investigators chair the Wilms Tumor Committee, the Neuroscience Subcommittee of the Brain Tumor Committee, and co-chair the Pathology Discipline Core Committee, as well as being active on a number of other POG Core Committees. They have made major contributions over the last few years in the areas of solid tumor oncology, neuro- oncology and the treatment of lymphoid malignancies. We are strongly committed to the interdisciplinary approach to pediatric cancer and have established collaboration with the necessary clinical specialties including Radiation Medicine, Pediatric Surgery, Pediatric Neurology, Neurosurgery, and Orthopedic Surgery, as well as with researchers in immunology, pharmacology and molecular biology. As more children are cured of their cancers, the identification and prevention, when feasible, of complications of therapy have become imperative. We have been a major contributor to the identification and understanding of the long-term medical and psychosocial effects of the treatment of leukemia, Hodgkin's disease, and a number of solid tumors, both through the cooperative group mechanism and through institutional studies.